SEVENTH ANNUAL REPORT. 139 
of this invagination of the wall of the vesicle. When these hol- 
low ingrowths are evaginated so as to form external appendages 
of the vesicle they present the form and armature of the cestode 
head, as well as a more or less developed neck, which presents 
a number of annulated rings, the first traces of future segmen- 
tation. 
The whole embryo now presents the form of a bladder or 
vesicle, with which it is connected at one point, a process having 
all the characters of the head and neck of the mature tapeworm, 
the head and neck constituting the scolex, while the cyst in which 
the bladder worm lies is known as an hydatid cyst. 
So long as the scolex remains attached and in the body of its 
host, it never develops into a sexually mature tapeworm, but 
must enter the alimentary canal of another animal of a different 
species. 
All hydatids get their nourishment by inhibition, absorbing it 
from the surrounding tissues; accidental destruction of vesicle 
destroys its integrity and the hydatid dies. The shepherds in 
Europe take advantage of this fact in treating sheep affected with 
hydatid disease, or sturdy gid, as it is familiarly called, by manip- 
ulating the head between and behind the ears, where they usually 
find a softening of the bones of the cranium. This softening is 
due to absorption of the bone from pressure of the growing 
hydatid; but, of course, this sign can only be observed when the 
hydatid is superficially situated. After location of the hydatid 
the cyst is punctured, allowing the fluid to escape, and the skin 
over the opening covered by means of a piece of sticking-plaster. 
DIFFERENTIATION OF HYDATIDS. 
As most hydatids to the naked eye appear very much the same, 
it is only by careful microscopic examination that the differences 
are noted and a safe conclusion drawn. As, for instance, the 
distinguishing features of the Cysticercus bovis, or beef hydatid, 
are: (1) its habitat, (2) large size of scolex, (3) the considerable 
pigmentary matter around its suckers, and (4) the absence of 
hooklets on head. For this latter peculiarity it has been named 
the unarmed hydatid and tapeworm. 
The cysts of Cysticercus cellulosa are elliptical, or flask-shaped. 
These are principally found in the muscular tissue of their host, 
the scolex being seen as a pearly white spot through the wall of 
its cyst. The cysts vary in size from a pea to that of a small 
